Screw



H. W. HACKER SCREW April 4, 1950 Filed 001;. 24, 1944 I INV EN TOR. 4 jzfi/zzcewaifr Patented Apr. 4, 1950 UNITED STATES PATENT OFFICE SCREW Horace W. Hacker, La Grange, Ill.

Application October 24, 1944, Serial No. 560,135

4 Claims.

This invention relates to fastening screws of the type that are provided with a screw driver receiving slot extending across the top face thereof through the circumference and open at both ends, and which slot receives a standard wedge-shaped screw driver bit.

In the operation of tightening or loosening a screw of the above type, against great resistance, one of the problems encountered is that of slipping of the screw driver bit along the slot. A related problem is that of burring and rounding the screw slot by the screw driver. It is an object of the present invention to provide a screw of the above mentioned type wherein these difiiculties are reduced or entirely eliminated.

When a turning force is applied to a standard screw by means of a standard screw driver the contact between the driver bit and the screw is at two points at the top edges of the slot, the slot being engaged by diametrically opposite corners of the screw driver bit. Due to the great unit pressure at the two points of contact the wedge-shaped screw driver bearing only on the sharp corners of the rectangular slot tends to burr and round the slot thereby defacing it into an objectionable appearance, and what is more important, reducing its power to grip the screw driver bit so that it becomes diflicult and sometimes impossible to drive the screw all the way home or to remove it by means of the screw driver. Furthermore, in view of the fact that the operator is rarely able to maintain the screw driver perfectly coaxial with the screw when he is exerting force on the screw driver, there is also a tendency for the end of the screw driver bit to slip along the bottom of the slot, thus causing more burrs and damaging the surrounding parts and slowing up the work.

In accordance with the principles of the present invention the above mentioned difficulties are eliminated when using a standard flat sided wedge-shaped screw driver on a screw constructed as hereinafter set forth. This is accomplished by making the sides of the screw slot tapered and at a greater angle than the angle of the wedge of the screw driver. The top of the slot is wider than the thickness of the tip of the screw driver and the bottom of the slot is narrower than the tip of the screw driver. As a result the tip of the screw driver extends into the screw slot for only part of the depth of the slot. The bottommost edges of the screw driver engage the sides of the slot in two lines along two converging planes for the full width of the screw driver bit. The driver bit does not touch the top corners of the slot at all. It bears in two line contacts within the slot and below the top. Thus there can be no burring at the surface, no rounding of the corners and no loss of power. Also the screw driver bit wedges in the slot, is firmly gripped, and has no tendency to slip.

The attainment of the above and further ob- 2 jects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a top view of a flat head wood screw embodying the present invention;

Figure 2 is a side view of the screw of Figure 1, with a screw driver positioned in the slot of the screw;

Figure 3 is a sectional view taken along the line 3-3 of Figure 2 and looking in the direction of the arrow;

Figure 4 is a sectional view taken along the line 4-4 of Figure 2;

Figure 5 is a side view of a screw of a modified construction;

Figure 6 is a top view of another screw of a, modified construction;

Figure '7 is a side view of the screw of Figure 6; and

Figure 8 is an enlarged cross sectional view taken along the line 8--8 of Figure 6.

Reference may now be had more particularly to the screw illustrated in Figures 1 to 4. The screw, indicated in general by the reference numeral I, as a wood screw having a usual shank 2 the lower part of which is threaded as at 3 to a point, so that in use the screw can form its own hole in the wood into which it is being threaded. The bottom surface of the head 4 is conical, as indicated at 5, and the top surface 6 is flat. A screw driver slot 1 is formed in the head 4 symmetrically along the longitudinal axis 8 of the screw. The slot 1 extends straight across the face 6 of the screw head. The opposite walls Ill-4i of the slot are flat planar surfaces inclined to the vertical and each making an angle approximately 10 with the aXis 8 or an angle of 20 with one another. The bottom I2 of the slot is a fiat planar surface.

The angle of inclination of the surfaces Ill-I l is one of the important features of the present invention. An understanding of the importance of this feature will be gathered from an analysis of the action of a screw driver in the slot 1 in turning the screw, especially against resistance. For this purpose consider a standard type of screw driver I5 having flat surfaces l6-ll which extend the width of the bit of the screw driver and which are inclined to one another approximately 10, each of said surfaces making an angle of approximately 5 with the longitudinal axial plane of the screw driver. The top of the slot 1 is of a width in excess of the thickness of the bottom of the screw driver bit, indicated at [8, and the width of the slot at its bottom surface i2 is less than the thickness of the bottom of the screw driver bit. The angle of inclination of the walls Ill and ll of the sides of the screw slot is appreciably greater than the angle of inclination of the opposite sides Iiill of the screw driver. As

a result when the bit of the screw driver is inserted into the slot of a screw the fiat base of the bit contacts the side walls I-ll of the screw slot along parallel lines of contact indicated at 2fl2l. When a turning force is applied to the screw driver that force is transmitted to the side walls lO-ll along lines of contact rather than along point contact. Due to the wedging action of the bottom of the screw driver into the slot, as a result of the difference in taper of the surfaces l6-l'l of the screw driver and the surfaces l0| I of the screw slot, the screw driver will not tend to slip in the screw slot.

D1 Figure I have shown a wood screw of the same type as that of Figure 2, differing therefrom only in that the slot side walls l8| l, which correspond to the side walls Ill-ll of Figure 2, are at a greater angle to one another and the depth of the slot is such that the walls l0-H' meet, as indicated at 24. The bottom of the screw slot of Figure 5 is therefore a straight line instead of a flat surface as at I2. The line 24 of intersection of the side walls lfii l passes through the longitudinal axis of the screw and is at right angles thereto.

In Figures 6, 7 and 8 there is shown a modified form of screw slot. In this embodiment of the present invention the tapered side walls IBH of the screw slot extend for only approximately the top half of the depth of the slot. The bottom half of the slot has flat side walls 38-3l which are inclined to one another at a substantially greater angle than the angle between the sides lU--l I. In one preferred construction the walls l0-l| make an angle of approximately 5 with the longitudinal axis of the screw, which is the same angle that the wedge sides l6|'i of a standard screw driver make with that axis, whereas the walls 303i each makes an angle of approximately 30 with that axis. As a result of this arrangement if a thick tipped screw driver is used it will engage the screw slot along the surfaces l[l'l l' whereas if a thin screw driver is used it will engage the screw slot along straight parallel lines on the surfaces 303I.

In compliance with the requirements of the patent statutes I have here shown and described a few preferred embodiments of my invention. It is, however, to be understood that the invention is not limited to the precise constructions here shown, the same being merely illustrative of the principles of the invention. What is considered new and. desired to be secured by Letters Patent is:

1. A fastening screw of the type having a head at one end thereof and a screw driver receiving slot extending in a straight line completely across the screw head, the two opposite sides of the slot being fiat surfaces inclined with respect to one another and symmetrical with respect to an axial plane parallel to the lengthwise direction of the slot, the slot being wider at its top than at its bottom and the included angle of the sides of the slot being more than said sides extending from the top of the slot for only a fractional part of the depth of the slot, the bottom sides of the slot being also flat and symmetrical with respect to the same axial plane and at a substantially greater angle to one another than the angle between the upper sides of the screw slot, so that upon insertion into the slot of the end of a wedgeshaped screw driver the sides of which are inclined to one another about 10 the end of the screw driver makes line contact With the walls 4 of the slot intermediate the top and the bottom of the slot.

2. A fastening screw of the type having a head at one end thereof and a screw driver receiving slot extending in a straight line completely across the screw head, the slot being wider at its top than at its bottom, the two opposite sides of the slot being flat surfaces inclined with respect to one another and symmetrical with respect to an axial plane parallel to the lengthwise direction of the slot, the upper part of said sides extending in one angle from the top of the slot for only a fractional part of the depth of the slot, the lower part of said sides of the slot being also flat and symmetrical with respect to the same axial plane and extending toward the bottom at a substantially greater angle than the angle between the upper sides of the slot.

3. A fastening screw of the type having a head at one end thereof and a screw driver receiving slot extending in a straight line completely across the screw head, the two opposite sides of the slot being flat surfaces inclined with respect to one another and symmetrical with respect to an axial plane parallel to the lengthwise direction of the slot, the slot being wider at its top than at its bottom, the upper part of said sides extending at an included angle of 10 from the top of the slot for only a fractional part of the depth of the slot, the lower part of said sides of the slot being also flat and extending for the remaining depth of the slot and being symmetrical with respect to the same axial plane and at a substantially greater angle to one another than the angle between the upper sides of the screw slot, so that upon insertion into the slot of the end of a screw driver bit of a 10 included angle and of a thickness to fit the upper part of the slot the sides of the screw driver bit will bear against the sides of the upper part of the slot in diametrically opposite lines substantially parallel to the longitudinal axis of the screw, and upon the insertion of a screw driver bit of a thickness substantially thinner than the width of the upper part of the slot the bottom edges of the screw driver bit will bear against the sides of the lower part of the slots in two parallel lines perpendicular to the longitudinal axis.

4. A fastening screw of the type having a head at one end and a screw driver receiving slot extending in a straight line completely across the screw head and completely through the screw at the top and at the bottom of the slot, the two opposite sides of the slot being symmetrical with respect to an axial plane parallel to the lenghwise direction of the slot, theslot being wider at its top than at its bottom, each of the sides of the slot extending from the top of the slot for only a fractional part of the slot at one inclination with respect to said axial plane and at a different and greater angle for the rest of the depth of the slot, the upper part of each slot side being flat and the lower part of each slot side also being fiat.

HORACE W. HACKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 391,097 Thayer 1 Oct. 16, 1888 2,058,197 West Oct. 20, 1936 2,160,244 West May 30, 1939 2,289,561- West July 14, 1942 

